The objectives of this project are to determine the incidence of elevated serum parathyroid hormone (PTH) concentration in patients with cancer, to follow the effect of therapy on serum PTH levels, to establish the source of serum PTH by venous catheterization studies, to learn which organs alter and metabolize PTH by studying serum obtained at catheterization, to determine what factors may alter PTH secretion by tumors in vivo and in vitro, and by establishing tissue cultures from cancer cells to investigate factors affecting PTH synthesis, DNA synthesis, and cell replication. PTH will be measured by a sensitive radioimmunoassay.